A Texas woman has been arrested in connection with the mailing of three letters containing a form of the poison ricin to President Obama, New York City Mayor Mike Bloomberg and the director of Mayors Against Illegal Guns, federal authorities said.

Shannon Rogers Guess Richardson of New Boston, Texas, originally called the Federal Bureau of Investigation claiming that her husband had sent the letters, officials said. The investigators found that she had sent the letters herself, they said.

Richardson is an actress with minor roles on television shows like The Walking Dead and the Vampire Diaries, and was arrested in Arkansas on charges that will be filed Friday afternoon, the authorities said. She has five sons, according to the New York Times.

Her husband, Nathaniel Richardson, is an Army veteran

Investigators have been probing who sent the three letters, all postmarked May 20 from Shreveport, La. and sent without a return address, authorities have said.

The letters sent to Obama and Bloomberg were discovered during routine mail screenings processes. The letter to the director of Mayors Against Illegal Guns, Mark Glaze, was opened.

“You will have to kill me and my family before you get my guns,” the message sent to Bloomberg read, according to NBC New York, which obtained a copy of the letter. “Anyone who wants to come to my house will get shot in the face. The right to bear arms is my constitutional God given right and I will exercise that right till the day I die.”

The toxin ricin can be made from castor beans, has no antidote, and takes about 36 hours to kill.

Mayors Against Illegal Guns is a group that advocates for stronger gun laws and was founded by Bloomberg.

“I trust the police department and I feel perfectly safe,” Bloomberg said regarding the threatening letters on his weekly radio show in May. “I’ve got more danger from lightning than from anything else and I’ll go about my business.”

In a separate case involving ricin in recent months, police arrested James Everett Dutschke, 41, on charges that he sent letters containing ricin to the president and other officials in a separate case. The martial arts instructor has pleaded not guilty, and his trial is set of July 29, Reuters reported.

NBC News

Letter addressed to New York Mayor Michael Bloomberg that was found to contain a form of the poison ricin. The letter is postmarked May 20 from Shreveport, La.

Related:

• Letter mailed to Pres. Obama tested positive for ricin
• Mayor Bloomberg on ricin letters: I feel perfectly safe
• Who sent ricin letters to Bloomberg, Obama?

AP file

This undated photo obtained from the facebook page of Paul Kevin Curtis, shows, according to neighbors, Paul Kevin Curtis, 45.

OXFORD, Miss. — Investigators haven't found any ricin in the house of a Mississippi man accused of mailing poisoned letters to President Barack Obama, a U.S. senator and a local judge, according to testimony Monday from an FBI agent.

Agent Brandon Grant said that a search of Paul Kevin Curtis' vehicle and house in Corinth, Miss., on Friday did not turn up ricin, ingredients for the poison, or devices used to make it. A search of Curtis' computers has found no evidence so far that he researched making ricin.

Defense lawyers for Curtis say investigators' failure to find any ricin means the government should release their client. That lack of physical evidence could loom large as a detention and preliminary hearing continues Tuesday morning. U.S. Magistrate Judge J. Allan Alexander ended the hearing after lunch Monday, citing a personal schedule conflict.

Through his lawyer, Curtis has denied involvement in letters sent to Obama, Mississippi Republican Sen. Roger Wicker, and a Lee County, Miss., judge. The first of the letters was found April 15.

"There was no apparent ricin, castor beans or any material there that could be used for the manufacturing, like a blender or something," Grant testified. He speculated that Curtis could have thrown away the processor. Grant said computer technicians are now doing a "deep dive" on the suspect's computers after initially finding no "dirty words" indicating Curtis had searched for information on ricin.

Christi McCoy, who is leading the defense for Curtis, said the government doesn't have probable cause to hold her client and his history of problems related to bipolar disorder are not enough to keep him in jail.

"The searches are concluded, not one single shred of evidence was found to indicate Kevin could have done this," McCoy told reporters after the hearing.

She questioned why Curtis would have signed the letters "I am KC and I approve this message," a phrase he had used on his Facebook page, and then thrown away a processor used to grind castor beans. And she said that in any event, Curtis is not enough of an imminent danger or flight risk to justify holding him without bail.

"If they continue to demand his incarceration, it's basically bad faith," McCoy said. "Now, surely they are satisfied that there is no immediate threat from Kevin Curtis, and we want him released."

McCoy said in court that someone may have framed Curtis, suggesting that a former business associate of Curtis' brother, a man with whom Curtis had an extended exchange of angry emails, may have set him up.

Still, Grant testified that authorities believe that they have the right suspect.

"Given the right mindset and the Internet and the acquisition of material, other people could be involved. However, given information right now, we believe we have the right individual," he said.

Grant said lab analysis shows the poison is a crude form that could have been created by grinding castor beans in a food processor or coffee grinder.

"That would be a low-tech way of doing it. You're just blending up the beans to get the ricin that's on the inside on the outside," Grant testified.

The detention and preliminary hearing began Friday in U.S. District Court in Oxford, Miss. More witnesses besides Grant are expected Tuesday.

Federal investigators believe the letters were mailed by Curtis, an Elvis impersonator who family members say suffers from bipolar disorder. He wore an orange jumpsuit from the Lafayette County Detention Center in court Monday, and was quiet and attentive, sometimes whispering to McCoy.

Grant testified Monday that processing codes printed on the letter indicated they had been mailed from Tupelo, and that investigators were still trying to figure out from the codes exactly where they had been mailed from.

Grant testified Friday that authorities tried to track down the sender of the letters by using a list of Wicker's constituents with the initials KC, the same initials in the letters. Grant said the list was whittled from thousands to about 100 when investigators isolated the ones who lived in an area that would have a Memphis, Tenn., postmark, which includes many places in north Mississippi. He said Wicker's staff recognized Curtis as someone who had written the senator before.

Grant also testified that there were indentations on the letters from where someone had written on another envelope that had been on top of them in a stack.

The indentations were analyzed under a light source and turned out to be for Curtis' former addresses in Booneville and Tupelo, though the street name in one of the addresses was spelled wrong, Grant said.

All the envelopes and stamps were self-adhesive, Grant said Monday, meaning they won't yield DNA evidence. He said thus far the envelopes and letters haven't yielded any fingerprints.

McCoy said the evidence linking the 45-year-old to the crime has hinged on his writings posted online, which were accessible to anyone.

Much of Monday's testimony focused on Curtis' prior run-ins with police and evidence about his mental health.

"The fact that this man may be suffering from a form of mental illness, how does this make it make it more likely than not that Mr. Curtis committed to these crimes?" McCoy asked.

Grant said that it didn't, but said past evidence about mental state, "helps establish a potential behavior background for Mr. Curtis, perhaps not realizing what he's doing."

NEW YORK -- The NYPD is warning New York banks to concentrate their security efforts on mailrooms after a letter bomb was sent to the CEO of Deutsche Bank in Frankfurt, Germany, NBC New York reported.

All New York banks are "being advised to take precautions" Wednesday after the device was detected in the mailroom of Deutsche Bank's headquarters overseas, an official said.

No one was injured.

According to NBC New York, the NYPD warning to bank security officials reads in part:"We have received a report of a confirmed mail (package) explosive device that was addressed and sent to ... Deutsche Bank in Frankfurt, Germany. The package was detected by X-ray technology inside the mail room. The package did not detonate."

Read the original story on NBC New York

NYPD officials are stepping up security around Deutsche Bank locations in the city. There was no immediate word on what individual or what group sent the apparent letter bomb, the official said.

"The FBI's Joint Terrorist Task Force is aware of the matter and is consulting with its partners in the law enforcement and intelligence community," FBI spokesman Jim Margolin said.

Germany's Deutsche Bank confirmed on Wednesday it had received a suspicious envelope and handed it over to the police for investigation. "We confirm that a suspicious envelope has been sent to Deutsche Bank," a spokesman for Germany's biggest lender said.

A police spokesman in Frankfurt declined to say what was in the envelope but said a bomb disposal expert had been sent to the headquarters of Deutsche Bank, Germany's largest bank.

Frankfurt police spokesman Alexander Kiessling said: "There was a piece of mail that arrived at Deutsche Bank that was noticed. It was noticed because it seemed unusual."

Ackermann is the face of capitalism in Germany and is one of the few senior managers in the country who is always surrounded by bodyguards. He is due to retire in May next year after more than 10 years at the helm of the bank. 

A U.S. law enforcement official told Reuters that the package had been discovered in a mailroom around 1 p.m. Frankfurt time (7 a.m. EST) and contained explosives and shrapnel.

The official said it carried a return address from the European Central Bank, which is also located in Germany's financial center.

Banking sources said the bank had stepped up security measures around the world.

NBC New York and Reuters contributed to this story.